The present invention relates generally to underground drilling machines. More particularly, the present invention relates to reamers for use in horizontal directional drilling.
Utility lines for water, electricity, gas, telephone, and cable television are often run underground for reasons of safety and aesthetics. Sometimes, the underground utilities can be buried in a trench that is subsequently back filled. However, trenching can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, alternative techniques such as horizontal directional drilling (HDD) are becoming increasingly more popular.
A typical horizontal directional drilling machine includes a frame on which is mounted a drive mechanism that can be slidably moved along the longitudinal axis of the frame. The drive mechanism is adapted to rotate a drill string about its longitudinal axis. The drill string comprises a series of drill pipes threaded together. Sliding movement of the drive mechanism along the frame, in concert with the rotation of the drill string, causes the drill string to be longitudinally advanced into or withdrawn from the ground.
In a typical horizontal directional drilling sequence, the horizontal directional drilling machine drills a hole into the ground at an oblique angle with respect to the ground surface. To remove cuttings and dirt during drilling, drilling fluid can be pumped by a pump system through the drill string, over a drill head (e.g., a cutting or boring tool) at the end of the drill string, and back up through the hole. After the drill head reaches a desired depth, the drill head is then directed along a substantially horizontal path to create a horizontal hole. Once the desired length of hole has been drilled, the drill head is then directed upwards to break through the ground surface, completing a pilot bore.
The diameter of the pilot bore so constructed typically must be enlarged. To accomplish this, a reamer (sometimes called a backreamer) is attached to the drill string which is pulled back along the path of the pilot hole, thus reaming out the hole to a larger diameter. The reamer usually includes a reaming or cutting surface on which is mounted cutting teeth or other cutting or grinding elements. It is also common to attach a utility line or other conduit product to the reamer so that the product is pulled through the hole behind the reamer as the reamer enlarges the hole.
When utilizing standard backreaming techniques a backreamer is pulled longitudinally along the path of the pilot bore. Under certain conditions, however, the backreamer may tend to deviate from the path defined by the pilot bore. For instance, typically the pilot bore and drill string lie in an arcuate shape. Therefore the longitudinal force being exerted on the drill string tends to straighten the drill string, especially when soil conditions require increased levels of force on the drill string. This straightening tendency can affect the location of the backreamer by pulling the reamer higher. In some jobs the backreamer may move as much as 12 to 18 inches from the pilot bore. Such inaccuracy can have negative effects particularly when a utility or natural obstacle such as a river is being avoided.
In other situations, where large diameter bores are being formed, the weight of the backreamer can cause deviation from the pilot bore. A backreamer can only be moved longitudinally along the pilot bore at a rate in proportion to the drilling fluid being pumped to the reamer and out of the pilot bore. Therefore, longitudinal progress may be very slow. A heavy backreamer in the right soils will tend to drop lower than the pilot bore as it rotates quickly but moves slowly longitudinally.
Typically, the limiting factor in the speed of operation for a backreamer is the flow capacity of the pump system that pumps the drilling fluid. The backreamer should only displace soil at a rate in proportion to the amount of drilling fluid being pumped and removed from the pilot bore. Reamers may include mixing elements which assist in mixing the drilling fluid with the dirt and cuttings to achieve an easily displaceable consistency. The mixing elements rotate along with the reamer. The mixing function of the mixing elements and, therefore, the speed of the entire backreaming operation improves when the mixing elements are rotated at faster spinning speeds (rpms).
Faster spinning speeds also increase the total power transferred to the reamer. The total power transferred is a function of spinning speed multiplied by torque. By increasing the spinning speed of the drill string, more power can be delivered to the backreamer.
Faster spinning speeds, however, are not always desirable. Although spinning the backreamer at higher speeds improves mixing and delivers more power to the backreamer, faster or excessive speeds can cause instability of the assembly, resulting in fluctuations in the drive torque, torque spikes, and vibrations which deleteriously affect the cutting action of the cutting elements on the reaming surface of the backreamer. Spinning the cutting surface at faster speeds may also cause difficulty in controlling the backreamer.
These drawbacks become more acute with larger backreamers, particularly for backreamers which produce bores in excess of 18 inches. The speed of an individual cutting element on a backreamer is determined by the rotational speed of the backreamer and the distance from the center of the backreamer to the cutting element. Therefore, cutting elements on larger backreamers will move faster at any given spinning speed than cutting elements on smaller backreamers. As a result, the cutting action of a large backreamer is more susceptible to the inefficient effects of faster spinning speeds.
A backreamer, then, may perform several functions including: mechanically cutting, grinding and loosening the soil to enlarge the pilot hole diameter, directing drilling fluid to assist in the cutting action, mixing the loosened soil with the drilling fluid such that the resulting slurry is a consistency that will flow out of the bore when displaced by whatever product is to be pulled in, and transferring the longitudinal force required to pull the product through the hole.
The amount of torque necessary to rotate a backreamer depends on several factors which include: the outer diameter of the backreamer, the difference between the diameter of the pilot hole and the outer diameter of the backreamer, the type of soil, the speed at which the backreamer is being rotated, and the longitudinal force being applied to the backreamer.
One aspect of the present invention relates to a backreamer assembly adapted to be rotated by a drill string. The backreamer assembly includes a reaming surface and a torque transfer gear system that transfers torque from the drill string to the reaming surface of the backreamer. The torque transfer gear system is preferably configured to drive the reaming surface at a different rotational speed than the drill string. In one embodiment, the torque transfer gear system includes one or more reduction gears that rotate the reaming surface at a slower rotational speed than the drill string.
Another aspect of the present invention relates to a planetary gear train for a backreamer. The planetary gear train allows the cutting surface of the backreamer to spin at a slower speed than the speed at which the drill string rotates, thereby supplying increased power to the backreamer without the deleterious effects of instability and excessive vibrations. The planetary gear train includes a sun gear which is coupled to the drill string and rotates at the same speed as the drill string. The sun gear engages a number of planet gears which in turn engage a ring gear. The ring gear has an outer reaming surface. By adjusting the relative diameters of the ring and sun gears, the reaming surface of the ring gear can be rotated at a smaller or larger fraction of the speed of the drill string. The planet gears are held in position by a carrier frame which does not rotate. The carrier frame may be prevented from rotating by means of anti-rotation members, by a ream string, or even by the product being pulled into the bore.
Another aspect of the present invention relates to a drive system for a backreamer with mixing elements. The drive system rotates the mixing elements at a faster speed than the cutting surface of the backreamer thereby improving the mixing function of the mixing elements without deleteriously affecting the cutting function of the backreamer.
A further aspect of the present invention relates to a method for reaming a pilot bore dug by horizontal directional drilling. The method includes rotating the drill string and a mixing element at a first speed while rotating the cutting or reaming surface of the backreamer at a second speed slower than the first speed.
Yet another aspect of the present invention relates to a backreamer adapted with an offset mount for steering the reamer as it is pulled or pushed through a pilot bore. The offset mount is rotatably coupled to the backreamer such that it may be held from rotating during operation of the backreamer. The offset mount is further configured to couple to a ream line such that the longitudinal axis of the ream line is not collinear with the axis of rotation of a drill string.
Another aspect of the present invention relates to a backreamer having an offset mount and two u-joints (i.e. universal joints), a first u-joint coupling the backreamer to a drill string and a second u-joint coupling the offset mount of the backreamer to a ream line. The u-joints assist in steering the backreamer by allowing a greater range of angles at which the backreamer may be tilted during operation.
A further aspect of the present invention relates to a method for steering a reamer during horizontal directional drilling. The method includes providing a reamer with a rotatable offset mount. The reamer is coupled to both a drill string and a ream line. Specifically, the ream line is coupled to the offset mount. Rotating and positioning the ream line controls the orientation plane of the offset mount, determining the plane in which subsequent steering corrections can be made. The ream line may, in coordination with the drilling machine, be used to control longitudinal forces applied to the offset mount thereby redirecting the reamer.
A further aspect of the present invention relates to a method for steering a reamer during horizontal directional drilling. The method includes placing u-joints at both a front end and a back end of a reamer equipped with an offset mount. The u-joints permit a greater range of angles at which the reamer may be positioned, thereby improving the steering control of the reamer.
Another aspect of the invention relates to an anchoring machine that connects to a ream string that is capable of controlling the orientation and direction of movement of a reamer equipped with an offset mount by applying longitudinal force on the ream string in forward or backward directions and by controlling rotational orientation of the offset mount.
A further aspect of the present invention relates to a method for steering a reamer during horizontal directional drilling. The method includes providing a reamer with a rotatable offset mount. The reamer is coupled to both a drill string and a ream line, the drill string being further coupled to a horizontal drilling machine and the ream line being coupled to an anchoring machine. Specifically, the ream line is coupled to the offset mount. Rotating and positioning the ream line, a function of the anchoring machine, controls the orientation plane of the offset mount, determining the plane in which subsequent steering corrections can be made. The anchoring machine can then be used, in coordination with the drilling machine to control force applied to the offset mount thereby redirecting the reamer.
Another aspect of the invention relates to a new method that involves drilling a pilot bore with a horizontal drilling machine, connecting a reamer having an offset mount to the drill string which extends through the pilot bore at an exit point such that the drill string will rotate cutting elements of the reamer, positioning an anchor machine that stores drill rod at the exit point of the pilot hole, connecting a ream string which consists of drill rods to the reamer by means of the offset mount such that the ream string does not rotate, connecting the ream string to the anchor machine, propelling the reamer back along the pilot hole by cooperation of the drilling machine and the anchor machine in a manner to control position of the reamer, the anchor machine adding to the length of the ream string while the drilling machine is reducing the length of the drill string, when the reamer exits at the entry point removing the reamer, connecting the ream string to the drilling machine thereby converting it effectively to the drill string, removing the anchor machine, connecting the product to the drill string at the exit point and pulling it in with the drilling machine.
A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed.